The present invention relates to an improved ergonomically friendly surface-treating tool in which a flat surface of a rotary pad engages the surface of a workpiece for the purpose of abrading or polishing it and more particularly to an improved random orbital sander.
By way of background, in operation, random orbital sanders create forces at the sanding surface which are transmitted back to the operator's hand and arm through a lever which is the height of the random orbital sander between the face of the sanding disc and the top of the casing at the vertical centerline of the sander. Therefore, if this height is as short as possible, the operator's effort in overcoming the forces produced at the face of the sanding disc are less than if the height was greater. In addition, there is a second force which must be overcome by the operator, namely, the force produced by the flexible dust discharge hose which acts through a lever arm having a length between the vertical centerline of the orbital sander and the outer end of the dust discharge fitting which conveys dust from the shroud. When any one of the foregoing two dimensions are lessened, the effort required by the operator in using an orbital sander is accordingly lessened. Also, it has been observed that lower heights of the compressed air inlet connection and the dust discharge tube outlet above a sanding surface result in less effort to operate the sander. When all of the foregoing distances are lessened, the effort involved in using the orbital sander is all the more lessened.
Furthermore, in the past the outer end of the dust discharge tube always accepted a flexible dust carrying hose at a horizontal attitude. This had the disadvantage that the horizontal dust carrying hose could droop downwardly and contact external bodies relatively close to the sander with the attendant creation of frictional drag which the operator had to overcome. In addition, when the outer end of the dust discharge tube was relatively far from the vertical centerline of the sander there was a relatively long lever arm through which the force created by the flexible hose at the outer end of the dust discharge tube acted.
In addition, insofar as known, in the past a fitting was utilized at the outer end of the dust discharge tube which effectively increased the length of the dust discharge tube and thus increased the dimension between the vertical centerline of the sander and the outer end of the dust discharge fitting with the attendant increase of the lever arm through which the force exerted by the flexible dust discharge tube acted.
In addition, insofar as known, the compressed air inlet valve structure was not capable of providing small increments of adjustment to the rotary speed of the sander.
In the type of random orbital sanders using central vacuum systems to carry away the abrasives and foreign particles, a high volume of air is drawn through the housing. This causes eddy currents at the various sharp edges including the edges of the eccentric housing which contains the bearings which mount the spindle to which the pad is attached. Abrasives and foreign particles may thus enter the bearing area because they are sucked in to this area because of changes in positive and negative pressures due to the operation of the tool. One attempt to reduce the amount of foreign matter entering the bearing area is shown in U.S. Pat. No. 4,854,085 which utilized a triple seal. This approach did increase the bearing life to a certain degree.